Suspects arrested for the abduction and beating death of a Washington man allegedly said they were punishing a sexual predator. But prosecutors aren't ready to buy their vigilante tale, because there are signs that greed -- and not payback -- motivated the killing.

When Dean Barker was found dead outside a vacant home in Graham on Sept. 8, his hands were tied behind his back, tape covered his mouth and a bandana was wrapped around his neck, station KOMO reported.

An autopsy revealed that the killers strangled and beat him to death.

Investigators concluded that the 51 year old had been kidnapped and robbed. They soon arrested four suspects -- two men and two women -- ranging in age from 17 to 33. Police issued a warrant to arrest a fifth suspect as well, the Associated Press reported

The women allegedly told police that Barker had sexually assaulted them recently while one of the men claimed the victim molested his 3-year-old daughter, ABC News reported.

Pierce County Prosecutor Mark Lindquist says their accusations against Barker aren't backed up by any evidence yet, according to KING 5 News. Instead, they might be trying to cover up for a robbery.

"At this point we don't know if this is a case of vigilante revenge, or if the allegations about the sexual assault are just cover story," Lundquist said. "Why wait until weeks after the alleged sexual assault? Why take the victim's watch? Why steal the victim's money?"

The suspects are Angela King, 24, William Barry, 33, Justin Mahaffey, 23, and Aileenah Horton, 17. Their bail is set at $2 million each and they have not been charged yet. The fifth accomplice Jeffrey W. Powell, II, 30, remains at large.